This invention relates to a seat belt retractor which locks a seat belt against extraction by the action of sudden acceleration.
A seat belt apparatus installed at the seat of an automobile or the like for the purpose of protecting a passenger at the occurrence of an emergency is so adapted that the seat belt is taken up by a retractor device, equipped with an emergency locking mechanism, attached to a reinforced member of the vehicle body. When the passenger has fastened the seat belt, movement of the passenger ordinarily is accompanied by extraction of the seat belt from the retractor device so that passenger movement will not be restrained. On the other hand, when an emergency situation such as a collision occurs, an impact force or the like is sensed and the emergency locking mechanism is actuated to halt the rotation of a reel shaft about which the seat belt has wound. This stops the extraction of the seat belt and restrains violent movement of the passenger, thereby protecting the passenger against injury.
Though the above described emergency locking mechanism is capable of reliably stopping the rotation of the reel shaft upon about which the seat belt has been wound, there are cases where an excess amount of the seat belt that has been taken up on the reel shaft is pulled out owing to tightening of the seat belt, despite the fact that rotation of the reel shaft has been halted.
The applicant has already filed a patent application (Japanese Patent Application No. 63-185522) for a seat belt retractor adapted to prevent extraction of a seat belt due to this tightening of the seat belt.
FIG. 6 is a diagram illustrating the seat belt retractor according to this previously filed patent application.
As shown in FIG. 6, the seat belt retractor includes first emergency locking means 5 having a ratchet wheel 3 coaxially and integrally attached to a reel shaft 2 which rotates freely in accordance with extraction and take up of a seat belt 1 wound upon a reel, and a locking member 4a capable of being positionally displaced to engage with or disengage from the ratchet wheel 3, the reel shaft being locked against rotation by engaging the locking member 4a with the ratchet wheel 3, and second emergency locking means 9 having a sliding clamp member 7 attached to a case 6 so as to be capable of sliding in the directions in which the seat belt 1 is pulled out and taken up, and a turning clamp member 8 disposed opposite the sliding clamp member 7 for clamping and locking the seat belt 1 by operating in association with the locking action of the first emergency locking means 5.
The second emergency locking means 9 shown in FIG. 6 has a link member 4b actuated by displacement of the locking member 4a toward the ratchet wheel 3.
With the seat belt retractor having this construction, pull out of the seat belt due to tightening is prevented, thereby providing a seat belt retractor having a higher degree of reliability.
However, it has been clarified that since the first emergency locking means 5 and second emergency locking means 9 are actuated via the common locking member 4b by relying upon the link member 4b, it is difficult to finely adjust the mutual actuation timing of the two locking mechanisms.